HALS are well known in the art, especially those based on a tetraalkylpiperidine molecule (see for example U.S. Pat. No. 4,426,471 and U.S. Pat. No. 4,426,472). The HALS are utilized to stabilize polymeric substances against degradation due to, for example, light, particularly ultraviolet (UV) light. In some polymeric substances, such as coating formulations, an acidic curing agent is utilized to cure the coating composition. Utilization of basic HALS can adversely effect the cure of the coating by reacting with the acidic curing agent. Therefore, a desirable HALS for use in such circumstances would have as low a basicity as possible to reduce or eliminate interaction with the acid cure.
U.S. Pat. No. 4,356,307 discloses cyclic imides and their use as stabilizers for plastics, especially polyolefins, against photo and/or thermal degradation. The cyclic imides are represented by the general formula: ##STR2## in which R represents a saturated or unsaturated, optionally alkyl- or alkenyl-substituted alkylene or cycloalkylene radical having 2-20 C-atoms and in which R' represents hydrogen or a substituent such as,
an alkyl radical having 1-20 C-atoms, PA1 an alkenyl radical having 3-5 C-atoms, PA1 an aralkyl radical having 7-12 C-atoms, PA1 --CH.sub.2 --CH.sub.2 --CN, PA1 --CH.sub.2 --CH.sub.2 --COO--alkyl, PA1 --CH.sub.2 --CH(CH.sub.3)--COO--alkyl, PA1 an acyl radical or --(CH.sub.2 --CH.sub.2 O).sub.n H, wherein n can be 1-10. PA1 an alkyl radical having 1-20 C-atoms, PA1 an alkenyl radical having 3-5 C-atoms, PA1 an aralkyl radical having 7-12 C-atoms, PA1 --CH.sub.2 --CH.sub.2 --CN, PA1 --CH.sub.2 CH.sub.2 --COO--alkyl, PA1 --CH.sub.2 --CH(CH.sub.3)--COO--alkyl, PA1 an acyl radical or --(CH.sub.2 --CH.sub.2 O).sub.n H, wherein n can be 1-10. PA1 an alkyl radical having 1-20 C-atoms with methyl being preferred, PA1 an alkenyl radical having 3-5 C-atoms, PA1 an aralkyl radical having 7-12 C-atoms, PA1 --CH.sub.2 --CH.sub.2 --CN, PA1 --CH.sub.2 --CH.sub.2 COO--alkyl, PA1 --CH.sub.2 --CH(CH.sub.3 --COO--alkyl, PA1 an acyl radical or --(CH.sub.2 --CH.sub.2 O).sub.n H, wherein n can be 1-10. PA1 an alkyl radical having 1-20 C-atoms, PA1 an alkenyl radical having 3-5 C-atoms, PA1 an aralkyl radical having 7-12 C-atoms, PA1 --CH.sub.2 --CH.sub.2 CN, PA1 --CH.sub.2 --CH.sub.2 --COO--alkyl, PA1 --CH.sub.2 --CH(CH.sub.3)--COO--alkyl, PA1 an acyl radical or --(CH.sub.2 O).sub.n H, wherein n can be 1-10.
Berner, G. and Rembold, M., "New Light Stabilizers for High-Solid Coatings", in: Parfit, G. D. and Partsis, A. V., Organic Coatings, Science and Technology (1984), pp. 55-85, TP 1175.S607, relates to the search for a HALS with low bascity for use with 1-package high-solid paints (see for example pp. 75 et. seq.).
U.S. Pat. No. 4,419,472 discloses ester mixtures of polyalkylpiperidine derivatives of the formulas: ##STR3## wherein R.sub.1 is hydrogen or methyl, R.sub.2 is hydrogen, C.sub.1-12 alkyl, C.sub.3-8 alkenyl, C.sub.7-11 aralkyl, cyanomethyl or C.sub.2-4 acyl, R.sub.3 is C.sub.1-18 alkylene, C.sub.2-18 oxaalkylene, C.sub.2-18 thiaalkylene, C.sub.2-18 azaalkylene or C.sub.2-8 alkenylene and R.sub.4 is C.sub.1-4 alkyl. These mixtures are disclosed as being suitable as stabilizers for plastics.
A significant contribution to the art would be a method for stabilizing a polymeric substrate, such as an acid catalyzed coating formulation, utilizing a HALS which has little or no effect on the cure (as measured by the Knoop hardness test). Such a contribution is provided by this invention.